The present invention concerns a set of tires for conventional passenger cars having a driving axle and a load-bearing axle, the tires which equip the drive wheels having different treads than the tires equipping the load-bearing wheels.
Such equipping is known. The applicant's French Patent 1 473 029 teaches that the stability of vehicles is improved and that the tendency to oversteer is attenuated if the drift of the tires mounted at the rear of the vehicle is less than the drift of the tires mounted at the front. Thus, in the case of fast, super-powerful vehicles, the best solution at the time consisted in equipping the rear and the front of the vehicle with tires of identical size but the coefficients of drift of which vary between the rear and the front, these coefficients of drift being obtained on basis of modifications in internal structure or modifications of the tread.
In addition to the fact that the front-position rear- position set is not the equivalent of the drive-axle load- bearing-axle set, the tires considered above are not tires especially designed for equipping a vehicle intended to travel on poorly adherent ground such as snow-covered, icy, wet or muddy ground.
On these vehicles, the driving axle is required to transfer a torque onto the poorly adherent ground in order to transmit movement to the vehicle and this transmission of the torque must be effected, if possible, with the least possible wear of the tread. As to the load-bearing axle, it participates only slightly in the presence of longitudinal forces, but it is, however, capable of contributing to good braking of the vehicle. On the other hand, it must contribute practically exclusively to the stability of the vehicle on ground of the type in question and, in particular, to the transverse road-holding of the vehicle, whether on a straight line or on curves.
Patent Application EP 0 194 069 is another example. It shows a train of radial tires of the same size and same internal structure for equipping a vehicle intended to travel on any ground and having at least one driving axle and one load-bearing axle.
The tires of the two axles are provided with treads having the same so-called V pattern, the tires of the driving axle having a direction of travel opposite that of the tires of the load-bearing axle, and these treads being provided with elements in relief or blocks provided with incisions made by knife, the incisions of the central row of blocks being transverse.
Such equipping does not make it possible to obtain the compromise of desired properties such as described above.